This invention relates to a novel process for the production of 2-aryl-3-chloro-4,5,6,7-tetrahydro-2H-indazoles. In the past, 3-chloroindazoles were typically produced by reacting indazolones with phosphorus oxychloride.
British Pat. No. 901,169 describes the preparation of a compound of Formula I by reaction of phosgene with caprolactam. ##STR1##
The preparation of imidoyl chlorides of Formula II is described in Chem. Ber., 95, 126 (1962). ##STR2## where R is alkyl, aryl, or acetyl; and
R' is alkyl or aryl. PA1 X is fluorine, chlorine, bromine, iodine, cyano, methoxy, or nitro, preferably fluorine, chlorine or bromine. PA1 a. Temperature: 100.degree.-180.degree. C PA1 b. Molar Ratio of Phosgene to Indazolone (IV): 0.1:1 to 20.0:1 PA1 c. Molar Ratio of Solvent to Indazolone (IV): 1:1 to 50:1 PA1 d. Pressure: 1 to 50 atmospheres PA1 e. Time: 1 to 20.0 hours PA1 a. Temperature: 130.degree.-160.degree. C PA1 b. Molar Ratio of Phosgene to Indazolone (IV): 1.0:1 to 1.5:1 PA1 c. Molar Ratio of Solvent to Indazolone (IV): 5:1 to 20:1 PA1 d. Pressure: 10 to 30 atmospheres PA1 e. Time: 1 to 10 hours
The use of phosphorus oxychloride to prepare 2-aryl-3-chloro-4,5,6,7-tetrahydro-2H-indazoles is disadvantageous because it produces undesired by-products (including inorganic phosphates) that contaminate the product and are difficult to remove. Moreover, the standard chlorinating reagents like PCl.sub.5, SOCl.sub.2, SO.sub.2 Cl.sub.2 are ineffective in preparing 2-aryl-3-chloro-4,5,6,7-tetrahydro-2H-indazoles from 2-aryl-1,2,4,5,6,7-hexahydro-3H-indazol-3-ones. Since these indazoles are quite useful as herbicides, a process is needed which produces them in high yields. According to the instant invention such a process has been unexpectedly discovered.